Regional Trend Removal

Use the Regional Trend Removal dialog to specify the trend removal options.

Regional Trend Removal dialog options

Regional Grid	The regional grid to use for detrending. This grid must completely overlap all grids used in the stitching process. Script Parameter: GRIDSTCH.REGIONAL
Points to use	Select "All Points", "Edge Points", "Overlap Points", or "Overlapping Edge Points" to use for Trend Calculations. Script Parameter: GRIDSTCH.REGTRCALC (0: All; 1: Edge; 2: Overlap; 3: Overlapping edges; default: 2).
(Maximum) Trend	Select a Trend Removal method: "None", "Static", "Slope", 2nd Order Trend and 3rd Order Trend. If the RMS Error Tolerance is specified, then each trend order, up to the specified order, will be tested, and only the lowest order required to reduce the RMS difference between the regional and the detrended grid below the tolerance is used. For instance: If T1 is the trend calculated for the input grid G1, and TR is the trend calculated for the regional grid GR, then RMS Tolerance > RMS Error( (GR – TR) – (G1 – T1)) or, stated another way, the input grid 1 is detrended using T1, then the trend from the regional is added. The error is now the difference between the regional and this retrended grid. If no RMS Error Tolerance is specified, then the specified trend is applied immediately. Script Parameter: GRIDSTCH.REGTREND (0: None, 1: Static, 2: Slope, 3: 2nd Order, 4: 3rd order; default: 4)
RMS error tolerance	See the notes above for (Maximum) Trend. Script Parameter: GRIDSTCH.REGERROR (default – left blank)
Subtract regional when done?	Normally, if the grids are to be warped to the regional, then it will be left in the final grid. However, the regional can be subtracted out following the stitching operation if this option is set to "yes". Script Parameter: GRIDSTCH.REGREMOVE (default "Yes")

Application Notes

Trend Order

The user may wish to remove a static shift or trend from one or both grids before stitching. The zero-order or static correction removes a single average value from the entire grid. The first-order correction removes a best-fitting plane or slope. Higher orders fit 2nd or 3rd order polynomials in X and Y.

Point Usage

The calculation for the correction may be done in one of four ways; using all the points in the grid, using the edge points, using only the points which overlap with the other grid, or using only the edge points which overlap with the other grid.

Interpolation

Trend calculation and removal are performed subsequent to any interpolation. (Interpolation is optional).

If "edge points" is selected, and there is more than one disjoint section in the grid data, then only the first section that the algorithm encounters is used in the calculation.